次世代超伝導加速空洞のための超伝導積層薄膜構造の基礎的研究

2019 Fiscal Year Annual Research Report

• Project/Area Number: 17H04839
• Research Institution: High Energy Accelerator Research Organization
• Principal Investigator: 久保 毅幸 大学共同利用機関法人高エネルギー加速器研究機構, 加速器研究施設, 助教 (30712666)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 超伝導 / 加速器 / 超伝導共振器 / 薄膜

Outline of Annual Research Achievements

ニオブ製の超伝導加速空洞の加速電場は限界に達しつつあり、次世代超伝導加速空洞開発が急務である。そこで、超伝導積層薄膜構造の導入による加速電場の大幅な(２倍以上の)向上を目指すことが本研究の目的である。申請者は世界で初めて各層の最適な厚みの評価方法を明らかにする等、積層薄膜構造の理論研究で世界を牽引してきた。この優位性を利用して実験的研究を推進する。本研究では、限られた予算を最大限有効に使うため、安価な小型単セル空洞で試験を繰り返し、膜厚に関する広大なパラメータ空間を探索し、理論との比較を行うとともに、最適膜厚を有する空洞の実験において磁束侵入磁場の大幅な向上を確認することを目標としている。本研究は将来の加速器計画の建設費及び維持費の大幅な軽減につながる。
これまでに、ニオブ製空洞6個、練習用の銅製空洞9個を製作済みである。1個の銅空洞と1個のNb空洞を共同研究者がいる仏国CEA Paris-Saclayに送り、先方が持つ技術を用いた成膜の検討を依頼した。また、3個のNb空洞を共同研究者がいる米国JLabに送り、内面処理を依頼した。更に2個の銅空洞と1個のNb空洞について、クーポン空洞を作成した。内面にニオブ３スズを成膜するためには、フランジ部までニオブで作られているタイプの空洞が追加で必要となるため、フランジ用のニオブ材を購入した。
ニオブ平板上にニオブ３スズ薄膜を生成し、超伝導転移温度の測定と磁束侵入磁場の測定を行った。これにより、昨年度に実施した窒化ニオブ薄膜-ニオブ平板の性能確認に続き、ニオブ３スズ薄膜-ニオブ平板上の性能の確認ができた。
超伝導のミクロな理論に基づき、超伝導積層薄膜構造に適用可能な表面抵抗の理論を構築した。

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

ニオブ平板上に窒化ニオブを成膜する技術に加え、ニオブ平板上にニオブ３スズを成膜する技術が出来、サンプル試験による性能向上を確認した。更に、既に多くの空洞が完成済みであり、窒化ニオブ、ニオブ３スズともに空洞内面への成膜を進める段階に入った。理論的な理解も大幅に前進している。

Strategy for Future Research Activity

空洞内面への一様な薄膜形成の技術開発を進める。空洞内面の観察等を通じて膜質の改善を進める。そして製膜後の空洞を用いて性能測定を実施する。また、不純物を多く含む場合の超伝導積層薄膜構造の膜厚の最適化について、超伝導のミクロな理論に基づき研究を進めたい。

Research Products

• [Int'l Joint Research] Old Dominion University/Jlab(米国)
  • Country Name: U.S.A.
  • Counterpart Institution: Old Dominion University/Jlab
• [Int'l Joint Research] CEA Paris-Saclay(フランス)
  • Country Name: FRANCE
  • Counterpart Institution: CEA Paris-Saclay
• [Journal Article] Weak-field dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density (2020)
  • Author(s): Takayuki Kubo
  • Journal Title: Physical Review Research Volume: 2 Pages: 013302
  • DOI: 10.1103/PhysRevResearch.2.013302
  • Peer Reviewed / Open Access
• [Journal Article] Vortex penetration field measurement system based on third-harmonic method for superconducting RF materials (2020)
  • Author(s): Hayato Ito, Hitoshi Hayano, Takayuki Kubo, and Takayuki Saeki
  • Journal Title: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Volume: 955 Pages: 163284
  • DOI: 10.1016/j.nima.2019.163284
  • Peer Reviewed
• [Journal Article] Field-dependent nonlinear surface resistance and its optimization by surfacenanostructuring in superconductors (2019)
  • Author(s): Takayuki Kubo and Alex Gurevich
  • Journal Title: Physical Review B Volume: 100 Pages: 064522
  • DOI: 10.1103/PhysRevB.100.064522
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Optimum multilayer coating of superconducting particle accelerator cavities and effects of thickness dependent material properties of thin films (2019)
  • Author(s): Takayuki Kubo
  • Journal Title: Japanese Journal of Applied Physics Volume: 58 Pages: 088001
  • DOI: 10.7567/1347-4065/ab2f0a
  • Peer Reviewed / Open Access
• [Journal Article] Physics and challenges of superconducting cavities for particle accelerators and theoretical implication towards higher performance: Invitation to the world of superconducting cavities (2019)
  • Author(s): Takayuki Kubo
  • Journal Title: TEION KOGAKU Volume: 54 Pages: 275, 282
  • DOI: 10.2221/jcsj.54.275
  • Peer Reviewed / Open Access
• [Journal Article] Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK (2019)
  • Author(s): H. Ito, H. Hayano, T. Kubo, T. Saeki, R. Katayama, Y. Iwashita, H. Tongu, R. Ito, T. Nagata, C. Z. Antoine
  • Journal Title: Proceedings of SRF2019 Volume: - Pages: 634, 638
  • DOI: 10.18429/JACoW-SRF2019-TUP078
  • Open Access / Int'l Joint Research
• [Journal Article] Fabrication of 3.0-GHz Single-cell Cavities for Thin-film Study (2019)
  • Author(s): T. Saeki, H. Hayano, T. Kubo, H. Inoue, R. Katayama, F. E. Hannon, R. Rimmer, A.-M. Valente-Feliciano, Y. Iwashita, H. Tongu, H. Ito
  • Journal Title: Proceedings of SRF2019 Volume: - Pages: 177, 181
  • DOI: 10.18429/JACoW-SRF2019-MOP054
  • Open Access / Int'l Joint Research
• [Journal Article] Nb3Sn Thin Film Coating Method for Superconducting Multilayered Structure (2019)
  • Author(s): R. Ito, T. Nagata, H. Hayano, R. Katayama, T. Kubo, T. Saeki, Y. Iwashita, H. Ito
  • Journal Title: Proceedings of SRF2019 Volume: - Pages: 630, 633
  • DOI: 10.18429/JACoW-SRF2019-TUP077
  • Open Access / Int'l Joint Research
• [Journal Article] Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO2 on Pure Nb Sunstrate (2019)
  • Author(s): R. Katayama, H. Hayano, T. Kubo, T. Saeki, C.Z. Antoine, H. Ito, R. Ito, Y. Iwashita, H. Tongu, T. Nagata
  • Journal Title: Proceedings of SRF2019 Volume: - Pages: 809, 811
  • DOI: 10.18429/JACoW-SRF2019-THFUA2
  • Open Access / Int'l Joint Research
• [Presentation] Theory of field-dependent dissipative nonlinear conductivity in superconducting resonators (2020)
  • Author(s): Takayuki Kubo
  • Organizer: 10th ACASC / 2nd Asian-ICMC / CSSJ Joint Conference, Okinawa Convention Center (Okinawa)
  • Int'l Joint Research
• [Presentation] Field-Dependent Nonlinear Surface Resistance and Its Optimization by Surface Nano-Structuring of the SRF Cavities (2019)
  • Author(s): Takayuki Kubo and Alex Gurevich
  • Organizer: SRF2019, Dresden (Germany)
  • Int'l Joint Research / Invited
• [Presentation] Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK (2019)
  • Author(s): H. Ito, H. Hayano, T. Kubo, T. Saeki, R. Katayama, Y. Iwashita, H. Tongu, R. Ito, T. Nagata, C. Z. Antoine
  • Organizer: SRF2019, Dresden (Germany)
  • Int'l Joint Research
• [Presentation] Fabrication of 3.0-GHz Single-cell Cavities for Thin-film Study (2019)
  • Author(s): T. Saeki, H. Hayano, T. Kubo, H. Inoue, R. Katayama, F. E. Hannon, R. Rimmer, A.-M. Valente-Feliciano, Y. Iwashita, H. Tongu, H. Ito
  • Organizer: SRF2019, Dresden (Germany)
  • Int'l Joint Research
• [Presentation] Nb3Sn Thin Film Coating Method for Superconducting Multilayered Structure (2019)
  • Author(s): R. Ito, T. Nagata, H. Hayano, R. Katayama, T. Kubo, T. Saeki, Y. Iwashita, H. Ito
  • Organizer: SRF2019, Dresden (Germany)
  • Int'l Joint Research
• [Presentation] Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO2 on Pure Nb Sunstrate (2019)
  • Author(s): R. Katayama, H. Hayano, T. Kubo, T. Saeki, C.Z. Antoine, H. Ito, R. Ito, Y. Iwashita, H. Tongu, T. Nagata
  • Organizer: SRF2019, Dresden (Germany)
  • Int'l Joint Research / Invited
• [Remarks] researchmap
  • URL: https://researchmap.jp/kubotaka
• [Remarks] Google Scholar
  • URL: https://scholar.google.com/citations?user=MN4RQIsAAAAJ&hl=ja